1) Field of the Invention
This invention relates to a wavelength division demultiplexing apparatus particularly suitable for use with a wavelength division multiplexing and demultiplexing apparatus of the arrayed waveguide grating (AWG) type, which is used for wavelength division multiplex communication.
2) Description of the Related Art
FIG. 28 is a block diagram showing a configuration of a common wavelength division multiplexing and demultiplexing apparatus of the AWG type. The wavelength division multiplexing and demultiplexing apparatus can function as any of a wavelength division multiplexing apparatus and a wavelength division demultiplexing apparatus. In the following description, a wavelength division multiplexing and demultiplexing apparatus is referred to as MUX/DEMUX and is used as a term signifying a wavelength division multiplexing apparatus or a wavelength demultiplexing apparatus unless otherwise specified. Further, description is given of a case wherein, taking notice principally of the demultiplexing function from between the multiplexing function and the demultiplexing function the MUX/DEMUX has, the MUX/DEMUX functions as a wavelength division demultiplexing apparatus. It is to be noted that the inputting and outputting directions of light when the wavelength division multiplexing function of the MUX/DEMUX operates are reverse to those when the wavelength division demultiplexing function of the MUX/DEMUX operates.
Referring to FIG. 28, the MUX/DEMUX 106 shown includes a single input waveguide 101, an input slab 102, a plurality of channel waveguides 103, an output slab 104, and n output waveguides 105 all formed on a substrate 100 such that the input waveguide 101, input slab 102, channel waveguides 103, output slab 104 and output waveguides 105 may have a relatively high refractive index or indexes when compared with that of a surrounding region 100A.
It is to be noted that, in the following description, a portion formed from a material which has a relatively high refractive index when compared with that of the region 100A is sometimes referred to as xe2x80x9ccorexe2x80x9d, and another portion formed from a material which has a relatively low refractive index and surrounding the core such as the region 100A is sometimes referred to as xe2x80x9ccladxe2x80x9d. The input waveguide 1, input slab 2, channel waveguides 3, output slab 4 and output waveguide 5 correspond to the core, and the region 100A surrounding the input waveguide 1, input slab 2, channel waveguides 3, output slab 4 and output waveguide 5 corresponds to the clad.
In the MUX/DEMUX 106 shown in FIG. 28, when light multiplexed in a wavelength region is inputted to the input waveguide 101 of the MUX/DEMUX 106, light split for different wavelengths is outputted from channels #1 to #n of the output waveguides 105. On the other hand, when light of a plurality of different wavelengths is inputted to the channels #1 to #n of the output waveguides 105, light in which the light of all of the wavelengths is bunched and multiplexed in a wavelength region is outputted from the input waveguide 101.
In the following, the configuration of the MUX/DEMUX 106 is described in comparison with the configuration of a conventional spectroscope (monochro-meter). The functions of the MUX/DEMUX 106 are implemented, for example, by not only AWG type devices shown in FIGS. 28 and 29(a) but also spectroscope type devices shown in FIGS. 35 and 29(b) and other devices.
FIG. 35 is a view showing an example of a configuration of a conventional spectroscope. Referring to FIG. 35, the spectroscope shown is of the bulk diffraction grating type, and it is generally difficult to reduce the pitch of a diffraction grating. In contrast, a spectroscope of the AWG type does not require the pitch, and it is only necessary to design the differences in length among waveguides which compose the AWG.
Meanwhile, FIG. 29(a) is a schematic view showing a core pattern of the waveguides of the MUX/DEMUX 106 of the AWG type and particularly shows core portions of the MUX/DEMUX 106. The components (elements or parts) 101 to 105 of the MUX/DEMUX 106 shown in FIG. 29(a) individually correspond to components of a spectroscope.
FIG. 29(c) is a view illustrating a corresponding relationship between the components of a wavelength division multiplexing and demultiplexing apparatus configured using waveguides and a conventional spectroscope. The corresponding relationship is described with reference to FIG. 35. The spectroscope 110 shown in FIG. 35 includes, in addition to a diffraction grating 113 with an uneven or rough surface, a single input optical fiber 111, an input collimate lens 112, a condenser lens 114, and n output optical fibers 115.
The input waveguide 101 which is a component of the MUX/DEMUX 106 (refer to FIG. 29(a)) diffuses and outputs wavelength division multiplexed laser light, which is an object of wavelength division demultiplexing, to the input slab 102 in the following stage. Further, as seen in FIG. 29(c), the input waveguide 101 functionally corresponds to the input optical fiber 111 of the spectroscope 110 in that it has a role of an incidence slit for spreading light. It is to be noted that FIG. 29(a) is a schematic view particularly showing core elements in the MUX/DEMUX 106.
Similarly, the input slab 102 diffuses light incoming to the input waveguide 101 and couples the diffused light to the channel waveguide 103 in the following stage. The input slab 102 corresponds to a function of the input collimate lens 112 in the spectroscope 110 (a function of aligning incoming light powers from the input optical fiber 111 and irradiating them upon the diffraction grating 113 in the following stage).
Meanwhile, the channel waveguides 103 which correspond to the diffraction grating 113 of the spectroscope 110 deflect light to a predetermined angle for each of wavelengths as hereinafter described, and the output slab 104 which corresponds to the condenser lens 114 condenses the lights outputted (outgoing or radiated) from and diffracted by the channel waveguides 103. The output waveguides 105 which correspond to the output optical fibers 115 cut part of a spectrum of the light outgoing from the output slab 104.
Here, the channel waveguides 103 are formed with different lengths such that the channel waveguide at the lowermost position of the MUX/DEMUX 106 shown in FIGS. 28 and 29(a) has the smallest length and any other channel waveguide at a higher position has a successively increasing length. The differences in length between adjacent ones of the channel waveguides are equal to one another. The channel waveguides perform significant operation in wavelength division (splitting of light for each wavelength) or wavelength division multiplexing. In the following, operation of the channel waveguides 103 is described.
FIGS. 30(a) and 30(b) are views showing three neighboring channel waveguides of a plurality of channel waveguides 103 of the MUX/DEMUXs 106 shown in FIGS. 28 and 29(a), respectively. Each of the channel waveguides 131 to 133 shown in FIGS. 30(a) and 30(b) has positions (dark points) of a xe2x80x9ccrestxe2x80x9d and positions (blank points) of a xe2x80x9chollowxe2x80x9d of a light wave. Here, where a light wave propagating in the channel waveguides 131 to 133 is represented by cos(xcex1) (xcex1 represents the phase), the xe2x80x9ccrestxe2x80x9d represents the position at which the phase xcex1 is 2xc3x97nxc3x97xcfx80 and the xe2x80x9chollowxe2x80x9d represents the position at which the phase xcex1 is (2n+1)xc3x97xcfx80. It is to be noted that n and xcfx80 represent a positive integer and the number xcfx80, respectively.
Accordingly, in each of FIGS. 31(a) and 31(b), the length between two adjacent xe2x80x9ccrestsxe2x80x9d is equal to the wavelength of the light wave propagating in the channel waveguides 131 to 133. In particular, the light wavelengths shown in FIGS. 30(a) and 30(b) are equal to xcex0 and xcex1, respectively.
FIG. 30(a) shows a phase of light when light which has a wavelength equal to a central wavelength in a light wavelength arrangement used for wavelength division multiplex transmission. The length of each of the channel waveguides 103 is designed such that an accurately integral number of waves of light of the central wavelength xcex0 among the wavelengths of the wavelength division multiplexed light may be included therein. More particularly, in the case of FIG. 30(a), the lengths of the channel waveguides 103 are designed such that nine waves of the central wavelength xcex0 are included in the shortest waveguide 131, ten waves of the central wavelength xcex0 are included in the middle waveguide 132, and eleven waves of the central wavelength xcex0 are included in the longest waveguide 133.
For example, as seen in FIG. 31, when the channels #1 to #11 are set in the order from a short wavelength band, the wavelength of the light set to the channel #6 corresponds to the central wavelength xcex0 described above.
In particular, as seen in FIG. 30(a), light waves which have a component of a central wavelength to be outputted from the waveguides 131 to 133 have the same phase at the position of a slab boundary line 142 between the output slab 104 and the waveguides 131 to 133. In other words, an equiphase wave surface p1 of the light waves of the wavelength xcex0 outputted from the channel waveguides 103 is perpendicular to the waveguides 131 to 133, and the lights outputted from the three waveguides 131 to 133 are diffracted to an accurately horizontal direction d1 with respect to the output azimuths of the waveguides 131 to 133.
However, as seen in FIG. 30(b), light waves of the wavelength xcex1 shorter by xcex94xcex than that of the central wavelength component do not have the same phase at the position of the slab boundary line 142 between the output slab 104 and the waveguides 131 to 133, but have the same phase at another position shifted in a unit of xcex94xcex among the neighboring waveguides 131 to 133. In other words, an equiphase wave surface p2 of the light waves of the wavelength xcex1 is not perpendicular to the waveguides 131 to 133, and also the lights outputted from the waveguides 131 to 133 are diffracted to an upper side direction d2 in FIG. 30(b).
It is to be noted that light waves whose wavelength is longer by xcex94xcex than the central wavelength xcex0 are diffracted to a lower side direction in FIG. 30(b) in accordance with a principle similar to that described above. Accordingly, since the diffraction direction (diffraction angle) by each of the channel waveguides 103 depends upon the value of the optical wavelength of the wavelength division multiplexed light, the channel waveguides 103 can demultiplex the wavelength division multiplexed light.
The output slab 104 condenses the lights diffracted in predetermined diffraction directions for the individual wavelengths and multiplexed by the channel waveguides 103 and supplies the condensed lights to the output waveguides 105 of corresponding channels.
On the contrary, if lights of particular wavelengths (usually, lights of a spectrum of a width smaller than the bandwidth of the MUX/DEMUX 106 are used for WDM communication) corresponding to lights to be outputted to the channels #1 to #n (for example, outputs of ch#1 to ch#11 shown in FIG. 31) are inputted to the output waveguides 105 (refer to FIG. 28) for the outputs of the channels #1 to #n, then all of the lights are multiplexed and outputted from the input waveguide 101 (refer to FIG. 28).
FIG. 31 illustrates an example of the spectral characteristic and the insertion loss of the MUX/DEMUX 106 described above with reference to FIGS. 28 and 29(a). If wavelength division multiplexed light for 11 channels (channel (ch) #1 to channel #11) is inputted to the input waveguide 101, then the output waveguides 105 outputs lights with such intensities as seen from the channels #1 to #11 of FIG. 31.
A basic configuration and operation of an AWG which is an apparatus relating to the present invention are disclosed, for example, in xe2x80x9cIEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS. VOL. 2 No. 2, pp.236-250 (1996)xe2x80x9d and so forth. The wavelength division multiplexing and demultiplexing apparatus according to the present invention is similar, in regard to the configuration, function and operation other than those of the characteristic part of the present invention, to those disclosed in the reference document mentioned above.
The insertion loss of the MUX/DEMUX 106 is a loss at which the transmission factor for each of the channels #1 to #n of the output waveguides 105 exhibits a maximum value, or in other words, a loss with a wavelength with which the loss is lowest with respect to input light, and differs among different channels. For example, as seen in FIG. 31, the insertion loss of the MUX/DEMUX 106 differs among the output channels (#1 to #n).
Such insertion loss as described above with reference to FIG. 31 occurs principally at a connection location between the input slab 102 and each of the channel waveguides 103 (refer to a slab boundary line 122 shown in FIG. 30; hereinafter referred to as node) and a node between each of the channel waveguides 103 and the output slab 104 (refer to the slab boundary line 142 shown in FIGS. 30(a) and 30(b)).
FIGS. 32(a) to 32(c) are views each illustrating a factor of occurrence of the insertion losses at the nodes between the input slab 102 and the channel waveguides 103 described above. Particularly, FIG. 32(a) shows essential part of the MUX/DEMUX 106, and FIG. 32(b) shows the input slab 102 in an enlarged scale while FIG. 32(c) shows the nodes between the input slab 102 and the channel waveguides 103 in a further enlarged scale.
If attention is paid to the slab boundary line 122 on which the nodes between the input slab 102 and the channel waveguides 103 are positioned as illustrated in FIG. 32(c), of light 8 advancing from the input slab 102 toward a channel waveguide 103, light 85 which is transmitted by the channel waveguide 103 is valid, but light which arrives at a gap portion 123 is scattered and makes invalid light 86 and therefore becomes loss.
As a first countermeasure for reducing such insertion loss as described above, it is a possible idea to use such an input slab 102-1 as shown in FIG. 33(a) as the input slab for the MUX/DEMUX 106 shown in FIG. 28. The input slab 102-1 shown in FIG. 33(a) has a reduced channel waveguide distance dc so that the connection loss of the channel waveguides 103 is reduced.
In particular, if the channel waveguide distance dc is reduced in a condition that the width w, the focal length f (distance from the channel waveguide center 21 to the incoming position of the channel waveguide 103) and the channel waveguide number are fixed as illustrated in FIG. 33(b), then the connection loss of the channel waveguides can be reduced.
In the following, subjects to be solved are described in paragraphs (1-1) to (1-3).
(1-1) In the MUX/DEMUX 106 shown in FIG. 28, however, since the shape of the nodes between the input slab 102 and the channel waveguides 103 and the shape of the nodes between the output slab 104 and the channel waveguides 103 are symmetrical to each other, if the channel waveguide distance dc (refer to FIG. 33(a)) between the channel waveguides 103 of the input slab 102 side is decreased, then also the distance (not shown) between the channel waveguides 103 of the output slab 104 side decreases. In this instance, a disadvantage occurs that, in the proximity of the output slab 104 described below, lights propagating in the channel waveguides 103 join together and interfere with each other.
In particular, an optical waveguide has a characteristic that, as a plurality of waveguides come close to each other to make the distance therebetween small, lights propagating in the waveguides join together. Therefore, if the distance between the channel waveguides 103 is made small, lights propagating in the channel waveguides 103 join together in the proximity of the output slab 104 and interfere with each other. Further, as shown in FIG. 30(b), the MUX/DEMUX 106 functions as a wavelength division multiplexing and demultiplexing apparatus since a phase difference is produced among lights propagating in the channel waveguides 131 to 133 at the output apertures 142 of the channel waveguides 131 to 133.
Here, if it is assumed that the distance between the channel waveguides 131 to 133 in the proximity of the output slab 104 decreases until lights propagating in the channel waveguides 131 to 133 join together, then the phase varies and the wavelength division demultiplexing function drops (depresses). Accordingly, the MUX/DEMUX 106 illustrated in FIG. 28 has a subject to be solved in that it is impossible to decrease the distance (channel waveguide distance dc shown in FIGS. 32(c) and 33(a)) between the nodes between the input slab 102 and the channel waveguides 103 and the distance (not shown) between the nodes between the output slab 104 and the channel waveguides 103 as means for reducing the insertion losses.
(1-2) As a second countermeasure for reducing the connection (scattering) loss of the input slab 102 and output slab 104 and the channel waveguides 103 shown in FIG. 28, it is a possible idea to form, for example, such channel waveguides 103-1 as shown in FIG. 34(a).
In particular, as seen in FIG. 34(a), at an input side node 107 at which the channel waveguides 103-1 are connected to the input slab 102, tapering connection branches 162 whose width reduces as the distance from the input slab 102 increases are formed (in the following description, such a pattern that the waveguide width changes smaller as with the tapering connection branches 162 is referred to as tapering pattern or tapering).
In the countermeasure illustrated in FIG. 34(a), the scattering loss of the input side node 107 decreases as the width with which the tapering connection branches 162 are connected to the input slab 102 increases.
However, in the MUX/DEMUX 106 to which the channel waveguides 103-1 having such tapering connection branches 162 as described above with reference to FIG. 34(a) are applied, such higher-order mode light as hereinafter described is excited in the tapering connection branches 162 formed between the input slab and the channel waveguides as hereinafter described, and the excited higher-order mode light is radiated to the outside of the channel waveguides (core), resulting in loss.
Light incoming to the tapering connection branch 162 from the input slab 102 propagates in the tapering connection branch 162 formed as a core while the intensity peak is split into two (at a location at which higher-order mode light is excited) and then joined back into one. In the process wherein the number of peaks varies, part of the light (which corresponds to the higher-order mode light) is radiated to the outside of the channel waveguide (core) 103-1, resulting in loss.
Accordingly, also the MUX/DEMUX to which the channel waveguide 103-1 shown in FIG. 34(a) is applied has a subject to be solved in that it suffers from intensity-demultiplex light loss of higher-order mode light radiated to the outside of the channel waveguide 103-1.
(1-3) As described in paragraph (1-1) above, it is necessary to prevent joining together of lights propagating in the channel waveguides 103 at the output apertures of the channel waveguides 103 and keep the phase difference (phase difference between lights which propagate, for example, in the channel waveguides 103 of FIG. 30(b)) from which wavelength division multiplexing and demultiplexing operations arise. To this end, it is demanded to keep the distance between the channel waveguides 103 of the output slab 104 side great.
Further, it is necessary to make the gap (for example, the gap portion 123 shown in FIG. 32(c)) small. To this end, it is demanded to make the distance between the channel waveguides 103 of the input slab 102 side (channel waveguide distance dc shown in FIGS. 32(c) and 33(a)) small.
It is an object of the present invention to provide a wavelength division multiplexing and demultiplexing apparatus of the type wherein the shapes of an input slab and an output slab are symmetrical to each other, by which, while the distance between channel waveguides at nodes between the output slab and the channel waveguides is kept great, the distance between the channel waveguides at nodes between the input slab and the channel waveguides can be made small thereby to reduce the loss.
It is another object of the present invention to provide a wavelength division demultiplexing apparatus which can suppress excitation of higher-order mode light to reduce the loss caused by such higher-order mode light.
In order to attain the object described above, according to an aspect of the present invention, there is provided a wavelength division demultiplexing apparatus, comprising a substrate, a first waveguide, disposed on the substrate, for propagating wavelength division multiplexed light having a plurality of wavelength components, a first slab, disposed on the substrate, for diffusing the wavelength division multiplexed light inputted from the first waveguide, a plurality of channel waveguides, disposed on the substrate and having a series of different waveguide lengths increasing with a predetermined difference, for receiving and propagating the wavelength division multiplexed light diffused by the first slab, separately from each other channel waveguide, a second slab, disposed on the substrate, for receiving the wavelength division multiplexed light separately propagated through the plural channel waveguides and demultiplexing the received wavelength division multiplexed light into the plurality of wavelength components with condensing each of the plural wavelength components, and a second waveguide, disposed on the substrate, for propagating the light demultiplexed by the second slab therein, the channel waveguides and the first slab being optically connected to each other at a number of nodes greater than the number of nodes at which the channel waveguides and the second slab are connected to each other.
According to another aspect of the present invention, there is provided a wavelength division demultiplexing apparatus, comprising a substrate, a first waveguide, disposed on the substrate, for propagating wavelength division multiplexed light having a plurality of wavelength components, a first slab, disposed on the substrate, for diffusing the wavelength division multiplexed light inputted from the first waveguide, a plurality of channel waveguides, disposed on the substrate and having a series of different waveguide lengths increasing with a predetermined difference, for receiving and propagating the wavelength division multiplexed light diffused in the first slab, separately from each other channel waveguide, a second slab, disposed on the substrate, for receiving the wavelength division multiplexed light separately propagated through the plural channel waveguides and demultiplexing the received wavelength division multiplexed light into the plurality of wavelength components with condensing each of the plural wavelength components, and a second waveguide, disposed on the substrate, for propagating the light demultiplexed by the second slab therein, each of the channel waveguides having, in the proximity of a portion thereof at which the channel waveguide is optically connected to the first slab, a plurality of branches or waveguides through core to which the wavelength division multiplexed light from the first slab is inputted and a merging portion formed integrally with the branches or waveguides through core for optically coupling the wavelength division multiplexed light from the branches or waveguides through core.
In this instance, preferably each of the branches or waveguides through core has a width with which higher-order mode light of the wavelength division multiplexed light inputted thereto is cut off, the higher-order mode light being light of a mode or modes higher than the zero order mode, and a coupling contact at the merging portion is formed with a width with which the higher-order mode light of the distributed light inputted thereto can be excited.
Further preferably, each of the branches or waveguides through core is formed with a width which decreases in a tapering fashion from a portion thereof adjacent the merging portion toward the first slab.
Each of the branches or waveguides through core may have a tapering portion having a width which decreases in a tapering fashion from a portion thereof adjacent the merging portion toward the first slab and a fixed small width waveguide having a substantially fixed width substantially equal to the width of the tapering portion at a position at which the tapering portion has the smallest width for optically connecting the first slab and the tapering portion to each other.
In this instance, a boundary interface of the first slab to each of the channel waveguides may be formed in an arc centered at the center of diffusion of the light diffused in and inputted from the first slab to the boundary interface, and each of the branches or waveguides through core may have a center axis disposed on an extension line from the center of diffusion.
According to a further aspect of the present invention, there is provided a wavelength division demultiplexing apparatus, comprising a substrate, a first waveguide, disposed on the substrate, for propagating wavelength division multiplexed light having a plurality of wavelength components, a first slab, disposed on the substrate, for diffusing the wavelength division multiplexed light inputted from the first waveguide, a plurality of channel waveguides, disposed on the substrate and having a series of different waveguide lengths increasing with a predetermined difference, for receiving and propagating the wavelength division multiplexed light diffused in the first slab, separately from each other channel waveguide, a second slab, disposed on the substrate, for receiving the wavelength division multiplexed light separately propagated through the plural channel waveguides and demultiplexing the received wavelength division multiplexed light into the plurality of wavelength components with condensing each of the plural wavelength components, and a second waveguide, disposed on the substrate, for propagating the light demultiplexed by the second slab therein, each of the channel waveguides having, in the proximity of a portion thereof at which the channel waveguide is optically connected to the first slab, a plurality of sets of primary coupling portions each including a plurality of primary branching connection branches for receiving the wavelength division multiplexed light from the first slab and a primary merging portion for optically coupling the wavelength division multiplexed light from the primary branching connection branches, and a secondary coupling portion including a plurality of secondary branching connection branches for receiving the wavelength division multiplexed light coupled by the primary coupling portions and a secondary merging portion for optically coupling the wavelength division multiplexed light from the secondary branching connection branches.
In this instance, preferably each of the branching connection branches has a width with which higher-order mode light of the wavelength division multiplexed light inputted thereto is cut off, and a coupling contact at the merging portion is formed with a width with which the higher-order mode light of the wavelength division multiplexed light inputted thereto can be excited.
Further, a boundary interface of the first slab to each of the channel waveguides may be formed in an arc centered at the center of diffusion of the light diffused in and inputted from the first slab to the boundary interface, and each of the channel waveguides in the proximity of a portion at which the channel waveguide is optically connected to the first slab may have a center axis disposed on an extension line from the center of diffusion. Meanwhile, each of the branching connection branches may be formed with a width which decreases in a tapering fashion from a portion thereof adjacent the merging portion toward the first slab.
Preferably, each of the branching connection branches has a tapering portion having a width which decreases in a tapering fashion from a portion thereof adjacent the merging portion toward the first slab and a fixed small width waveguide having a substantially fixed width substantially equal to the width of the tapering portion at a position at which the tapering portion has the smallest width for optically connecting the first slab and the tapering portion to each other.
According a still further aspect of the present invention, there is provided a wavelength division demultiplexing apparatus, comprising a substrate, a first waveguide, disposed on the substrate, for propagating wavelength division multiplexed light having a plurality of wavelength components, a first slab, disposed on the substrate, for diffusing the wavelength division multiplexed light inputted from the first waveguide, a plurality of channel waveguides, disposed on the substrate and having a series of different waveguide lengths increasing with a predetermined difference, for receiving and propagating the wavelength division multiplexed light diffused in the first slab, separately from each other channel waveguide, a second slab, disposed on the substrate, for receiving the wavelength division multiplexed light separately propagated through the plural channel waveguides and demultiplexing the received wavelength division multiplexed light into the plurality of wavelength components with condensing each of the plural wavelength components, and a second waveguide, disposed on the substrate, for propagating the light demultiplexed by the second slab therein, each of the channel waveguides being formed such that a node thereof to the first slab has a width with which higher-order mode light of the separated light can be excited and the width thereof decreases in a tapering fashion away from the first slab, an island-shaped formation region of a reflection index lower than that of the channel waveguides being provided for each of the channel waveguides in such a manner as to partition the channel waveguide in the proximity thereof at which the channel waveguide is optically connected to the first slab into a plurality of waveguide portions.
In this instance, each of the waveguide portions of each of the channel waveguides partitioned by the island-shaped region may be formed as a waveguide by which higher-order mode light of the wavelength division multiplexed light inputted thereto is cut off, and the waveguide width at a portion at which the partitioned waveguide portions are coupled to each other may have a width with which the higher-order mode light of the distributed light inputted thereto can be excited.
Further, in the wavelength division demultiplexing apparatus, a boundary interface of the first slab to each of the channel waveguides may formed in an arc centered at the center of diffusion of the light diffused in and inputted from the first slab to the boundary interface, and further, each of the channel waveguides in the proximity of a portion at which the channel waveguide is optically connected to the first slab may have a center axis disposed on an extension line from the center of diffusion.
According to a yet further aspect of the present invention, there is provided a wavelength division demultiplexing apparatus, comprising a substrate, a first waveguide, disposed on the substrate, for propagating wavelength division multiplexed light having a plurality of wavelength components, a first slab, disposed on the substrate, for diffusing the wavelength division multiplexed light inputted from the first waveguide, a plurality of channel waveguides, disposed on the substrate and having a series of different waveguide lengths increasing with a predetermined difference, for receiving and propagating the wavelength division multiplexed light diffused in the first slab, separately from each other channel waveguide, a second slab, disposed on the substrate, for receiving the wavelength division multiplexed light separately propagated through the plural channel waveguides and demultiplexing the received wavelength division multiplexed light into the plurality of wavelength components with condensing each of the plural wavelength components, and a second waveguide, disposed on the substrate, for propagating the light demultiplexed by the second slab therein, each of the channel waveguides including, in the proximity of a portion thereof at which the channel waveguide is optically connected to the first slab, a plurality of coupling waveguides connected in tandem in a plurality of stages in a tree-like configuration for optically coupling and propagating the distributed light inputted thereto.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.